The Good Friday Experiment, also called the Marsh Chapel Experiment, tested whether psilocybin taken by religious people in a religious setting could produce mystical-type experiences. Walter Pahnke ran it for his Harvard doctorate, with Timothy Leary as adviser; 20 Protestant divinity students were sorted into matched pairs and one of each pair got psilocybin, the other nicotinic acid as an active placebo (Doblin, 1991). A 2025 commentary dates it to 20 April 1962 (Simonsson and Goldberg, 2025).
By Pahnke’s cut-off, four of the ten given psilocybin had a complete mystical experience and none of the controls did (Doblin, 1991). Rick Doblin’s follow-up, interviewing 16 participants in 1986–89, found the reports had lasted. It also found that every participant knew his group by the end of the day, and that one participant had been given an injected tranquilizer, which Pahnke never reported (Doblin, 1991).
Pahnke’s questionnaire became the ancestor of the Mystical Experience Questionnaire used today (Mosurinjohn et al., 2023), and a 2006 Johns Hopkins study was designed as a stronger replication (Griffiths et al., 2006).
Sources
- Doblin, 1991: Pahnke’s Good Friday Experiment, a long-term follow-up (MAPS copy)
- Simonsson and Goldberg, 2025
- Mosurinjohn, Roseman and Girn, 2023
- Griffiths et al., 2006, Psychopharmacology
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